Formate dehydrogenase has been partially purified from two strictly anaerobic bacteria, Clostridium sticklandii and Methanococcus vannielii. The enzyme from M. vannielii is soluble, whereas the enzyme in C. sticklandii is membrane bound and is solubilized from the pellet fraction of whole cell sonicates by various ionic and non-ionic detergents, such as SDS and triton X-100. Activity stains on disc gels show multiple formate dehydrogenase bands from both sources. The enzymes from both organisms are similar in that they have a temperature optimum at 65 degrees C, are extremely oxygen labile, are inhibited by cyanide, and have a bimodal pH optimum.